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The Universe can be a bit like a magic trick. As you move around to look at the different wavelengths of light, you can see all kinds of objects, events, and interactions that are otherwise invisible to the human eye.
Using New Mexico’s Very Large Array telescope, astronomers led by Marie-Lou Gendron-Marsolais of the European Southern Observatory scanned a huge cluster of galaxies. There in low-frequency radio wavelengths, they saw the complex invisible halos that could be the result of intense galactic interactions.
There is much more to a galaxy than the visible light it gives off. Many, including the Milky Way, have large-scale radio structures, vast bubbles, or radio emission jets extending far above and below the galactic plane. In many cases, these lobes and jets are well defined and more or less symmetrical.
In the Perseus cluster, located in the constellation Perseus some 240 million light-years from the Milky Way, a different picture emerges.
The Perseus cluster is enormous, one of the most massive objects in the known universe. It contains thousands of galaxies enveloped in a huge cloud of hot gas. And the new VLA images – the first in high resolution in the low frequency range of 230 to 470 mergahertz – reveal unheard of detail in large-scale radio structures.
The galaxy NGC 1275, also known as Perseus A, sits right in the center of the cluster, and it’s the brightest galaxy there. In its inner lobes, observations reveal new substructures – thin radio-emitting filaments and loop-like structures in the southern lobe. Observations also confirmed the presence of radio spurs in the outer lobes, first detected in 2002.
Meanwhile, the galaxy NGC 1265 has two long jets – but they are bent at 90-degree angles, trailing in a single, curving, comet-shaped tail. This structure is well known, but confusing; these tails are generally interpreted as tracers of movement through the intracluster medium, caused by piston pressure. Based on an analysis of the difference in brightness in the tail, the team interprets this shape as evidence of two distinct electron populations.
They also identified new radio emission filaments in the tail, although at this point it is difficult to say what created them. It could have been turbulence or magnetic fields; higher resolution images will be needed for more detailed analysis.
Galaxy IC 310 is also a tailed galaxy, although its tail is straight which is much more normal, consistent with a radio galaxy falling into the cluster. But recent research has revealed that this galaxy is a blazar, with a jet of matter shooting at near-light speed from the galactic core towards the observer (that’s us here on Earth).
Due to the viewing angle, the team was able to observe gamma radiation from the galactic center, as well as new structures in the tail jets – two separate and tightly collimated jets at the base of the tail. According to their analysis, the observations are consistent with a blazaar, implying that bent-jet radio-galaxies and blazars are not mutually exclusive.
Clusters of galaxies are strange places, filled with interactions and objects that we don’t fully understand at all. These new observations are a breadcrumb trail on the learning trail… but they also underline the importance of getting there with the most powerful telescopes we can muster.
“These images,” said Gendron-Marsolais, “show us unseen structures and details and this helps us determine the nature of these objects”.
The team’s research was accepted in the Monthly notices from the Royal Astronomical Society, and is available on arXiv.
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